Every calculation Giraffe runs about your site starts with one shape: the project boundary. Get it right, and your site area, FSR, and open space numbers are trustworthy. Skip it, or draw it wrong, and those numbers are wrong too, or missing entirely.
What the boundary drives
Site area, calculated directly from the boundary's geometry.
If you manually override the site area in a project's properties, that value takes priority over the boundary's actual geometry.
FSR (Floor Space Ratio): total floor area divided by site area.
Open space and building coverage ratios: your site area, minus building footprints and hardscape.
The Urban app's site calculations. They don't run at all until you have a boundary, and Giraffe warns you if you draw features outside it, since that throws off your site coverage numbers.
Custom Analytics site measures: your building, landscape, and paving data gets clipped to the boundary before Giraffe calculates.
Precinct scenario tables, which flag any building drawn outside the boundary as an error.
What else it does
Sets your project's map origin, so coordinates line up correctly.
Can be used to clip or filter which map layers render.
Cut & Fill terrain calculations can be clipped to the boundary, or turned off entirely if you don't have one.
Boundary types
The boundary is shown as a thick grey dashed line, always visible in your project. A project's boundary can take one of three shapes, and which one you end up with depends on how you set it.
Polygon: this is a single, continuous shape. It's the standard boundary for one parcel or a contiguous site, and it's what you get when you draw a boundary manually or set it to a single map element. Most site calculations expect this. | 
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MultiPolygon: this is a boundary made of more than one separate shape. Each shape stays distinct on the map, and Giraffe treats them as one project for calculations, adding their areas together. Use it when your project spans multiple non-contiguous parcels, like a scattered land assemblage. Giraffe creates one automatically when you add another shape to your boundary (right-click Add to project boundary), or when you create a project from Data Table shapes that aren't touching. Site calculations run across every shape together. | 
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Point: this marks a single location, with no area. It's what you get if you drop a pin instead of drawing a boundary. It's useful for marking a site before you're ready to commit to an exact shape. It's also a placeholder: Giraffe won't run site calculations like FSR or open space ratio until you replace it with a real boundary. The Urban app prompts you to draw one before it calculates anything. | 
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The Project Boundary layer
Every project has a Project Boundary layer in the Layer Palette. Use it to show or hide the project boundary, change how it looks, or jump into editing it.
Click the eye icon on the Project Boundary layer to show or hide the boundary on the map.
Right-click the Project Boundary layer to choose Edit boundary, Edit style…, Hide or Show, or Zoom to boundary.
The layer's name shows the state of the boundary. It reads Project Boundary (Not drawn) when the project has no boundary yet, and Project Boundary (Editing) while the boundary editor is open.
Hiding the project boundary only changes what you see on the map. Site area, FSR, and other site calculations still use the boundary.
Create, edit, or style a boundary
See Create a Boundary to set a boundary for a new project, or Edit the Boundary to adjust one you've already set.